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Bug #46165 server crash in dbug

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This crash occured if the same debug trace file was closed twice,
leading to the same memory being free'd twice. This could occur
if the "debug" server system variable refered to the same trace
file in both global and session scope.

Example of an order of events that would lead to a crash:
1) Enable debug tracing to a trace file (global scope)
2) Enable debug tracing to the same trace file (session scope)
3) Reset debug settings (global scope)
4) Reset debug settings (session scope)

This caused a crash because the trace file was, by mistake, closed
in 3), leading to the same memory being free'd twice when the file
was closed again in 4).

Internally, the debug settings are stored in a stack, with session
settings (if any) on top and the global settings below. Each connection
has its own stack. When a set of settings is changed, it must be 
determined if its debug trace file is to be closed. Before, this was done
by only checking below on the settings stack. So if the global settings
were changed, an existing debug trace file reference in session settings
would be missed. This caused the file to be closed even if it was in use,
leading to a crash later when it was closed again.

This patch fixes the problem by preventing the trace file from being shared
between global and session settings. If session debug settings are set without
specifying a new trace file, stderr is used for output. This is a change
in behaviour and should be reflected in the documentation.

Test case added to variables.test.
This commit is contained in:
Jon Olav Hauglid 2010-09-28 11:07:58 +02:00
parent 71affc142d
commit 92b247814a
3 changed files with 127 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
dbug/dbug.c
View File

@ -515,11 +515,16 @@ int DbugParse(CODE_STATE *cs, const char *control)
stack->maxdepth= stack->next->maxdepth;
stack->sub_level= stack->next->sub_level;
strcpy(stack->name, stack->next->name);
stack->out_file= stack->next->out_file;
stack->prof_file= stack->next->prof_file;
if (stack->next == &init_settings)
{
/* never share with the global parent - it can change under your feet */
/*
Never share with the global parent - it can change under your feet.
Reset out_file to stderr to prevent sharing of trace files between
global and session settings.
*/
stack->out_file= stderr;
stack->functions= ListCopy(init_settings.functions);
stack->p_functions= ListCopy(init_settings.p_functions);
stack->keywords= ListCopy(init_settings.keywords);
@ -527,6 +532,7 @@ int DbugParse(CODE_STATE *cs, const char *control)
}
else
{
stack->out_file= stack->next->out_file;
stack->functions= stack->next->functions;
stack->p_functions= stack->next->p_functions;
stack->keywords= stack->next->keywords;

44
mysql-test/r/variables.result
View File

@ -1699,3 +1699,47 @@ set @@session.autocommit=t1_min(), @@session.autocommit=t1_max(),
drop table t1;
drop function t1_min;
drop function t1_max;
#
# Bug#46165 server crash in dbug
#
SET @old_globaldebug = @@global.debug;
SET @old_sessiondebug= @@session.debug;
# Test 1 - Bug test case, single connection
SET GLOBAL debug= '+O,../../log/bug46165.1.trace';
SET SESSION debug= '-d:-t:-i';
SET GLOBAL debug= '';
SET SESSION debug= '';
# Test 2 - Bug test case, two connections
# Connection default
SET GLOBAL debug= '+O,../../log/bug46165.2.trace';
SET SESSION debug= '-d:-t:-i';
# Connection con1
SET GLOBAL debug= '';
# Connection default
SET SESSION debug= '';
# Connection con1
# Connection default
SET GLOBAL debug= '';
# Test 3 - Active session trace file on disconnect
# Connection con1
SET GLOBAL debug= '+O,../../log/bug46165.3.trace';
SET SESSION debug= '-d:-t:-i';
SET GLOBAL debug= '';
# Test 4 - Active session trace file on two connections
# Connection default
SET GLOBAL debug= '+O,../../log/bug46165.4.trace';
SET SESSION debug= '-d:-t:-i';
# Connection con1
SET SESSION debug= '-d:-t:-i';
SET GLOBAL debug= '';
SET SESSION debug= '';
# Connection default
SET SESSION debug= '';
# Connection con1
# Connection default
# Test 5 - Different trace files
SET SESSION debug= '+O,../../log/bug46165.5.trace';
SET SESSION debug= '+O,../../log/bug46165.6.trace';
SET SESSION debug= '-O';
SET GLOBAL debug= @old_globaldebug;
SET SESSION debug= @old_sessiondebug;

75
mysql-test/t/variables.test
View File

@ -1432,3 +1432,78 @@ drop function t1_max;
###########################################################################
--echo #
--echo # Bug#46165 server crash in dbug
--echo #
SET @old_globaldebug = @@global.debug;
SET @old_sessiondebug= @@session.debug;
--echo # Test 1 - Bug test case, single connection
SET GLOBAL debug= '+O,../../log/bug46165.1.trace';
SET SESSION debug= '-d:-t:-i';
SET GLOBAL debug= '';
SET SESSION debug= '';
--echo # Test 2 - Bug test case, two connections
--echo # Connection default
connection default;
SET GLOBAL debug= '+O,../../log/bug46165.2.trace';
SET SESSION debug= '-d:-t:-i';
--echo # Connection con1
connect (con1, localhost, root);
SET GLOBAL debug= '';
--echo # Connection default
connection default;
SET SESSION debug= '';
--echo # Connection con1
connection con1;
disconnect con1;
--source include/wait_until_disconnected.inc
--echo # Connection default
connection default;
SET GLOBAL debug= '';
--echo # Test 3 - Active session trace file on disconnect
--echo # Connection con1
connect (con1, localhost, root);
SET GLOBAL debug= '+O,../../log/bug46165.3.trace';
SET SESSION debug= '-d:-t:-i';
SET GLOBAL debug= '';
disconnect con1;
--source include/wait_until_disconnected.inc
--echo # Test 4 - Active session trace file on two connections
--echo # Connection default
connection default;
SET GLOBAL debug= '+O,../../log/bug46165.4.trace';
SET SESSION debug= '-d:-t:-i';
--echo # Connection con1
connect (con1, localhost, root);
SET SESSION debug= '-d:-t:-i';
SET GLOBAL debug= '';
SET SESSION debug= '';
--echo # Connection default
connection default;
SET SESSION debug= '';
--echo # Connection con1
connection con1;
disconnect con1;
--source include/wait_until_disconnected.inc
--echo # Connection default
connection default;
--echo # Test 5 - Different trace files
SET SESSION debug= '+O,../../log/bug46165.5.trace';
SET SESSION debug= '+O,../../log/bug46165.6.trace';
SET SESSION debug= '-O';
SET GLOBAL debug= @old_globaldebug;
SET SESSION debug= @old_sessiondebug;